Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-09-21
2002-06-18
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06406146
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention pertains to method and apparatus for measuring optical quality of an eye. In particular, the present invention pertains to method and apparatus which measures refractive errors of an eye based on wavefront measurement.
BACKGROUND OF THE INVENTION
As is well known, a refractor is an optical apparatus used to measure refractive errors of an eye. In particular, a wavefront refractor is a refractor based on wavefront measurement, and as is further well known, a Hartmann-Shack wavefront sensor can be used to construct such a wavefront refractor.
FIG. 2
shows a block diagram of prior art wavefront refractor
200
. As shown in
FIG. 2
, wavefront refractor
200
comprises probe beam assembly
10
, polarizing beamsplitter
20
, relay optics assembly
40
, and Hartmann-Shack sensor assembly
50
′. As shown in
FIG. 2
, probe beam assembly
10
comprises a radiation source (not shown) which outputs beam of radiation
11
, which beam of radiation
11
(after being redirected by turning reflector
12
) is applied as input to polarizing beamsplitter
20
. Beam of radiation
11
typically comprises radiation that is not detected by a patient such as, for example, infrared or near infrared radiation. The source of beam of radiation
11
may be a super-luminescent diode or a laser. The beam of radiation output from polarizing beamsplitter
20
is directed to impinge upon eye
30
to form illumination spot
32
on retina
31
.
As shown in
FIG. 2
, radiation scattered from illumination spot
32
passes through the eye's optics (including eye lens
34
and cornea
35
), and emerges as outgoing beam
33
. The wavefront of outgoing beam
33
carries aberration information directly relating to the optical quality of the eye's optics. For example, for a perfect emmetropic eye without aberration error, the wavefront of outgoing beam
33
is a flat plane; for a myopic or hyperopic eye, the wavefront of outgoing beam
33
has the shape of a spherical surface; and for an eye with high order aberrations, the wavefront of outgoing beam
33
is distorted irregularly.
As shown in
FIG. 2
, relay optics assembly
40
relays the wavefront of outgoing beam
33
from exit pupil plane P of eye
30
to Hartmann-Shack sensor assembly
50
′ disposed at conjugate plane P′. As further shown in
FIG. 2
, Hartmann-Shack sensor assembly
50
′ of prior art wavefront refractor
200
comprises lenslet array
51
and CCD camera
53
. The principles and design parameters used to fabricate Hartmann-Shack sensor assembly
50
′ are well known in the art. In accordance with the prior art design, CCD camera
53
is located at the focal plane of the lenslet elements of lenslet array
51
, and prior art Hartmann-Shack sensor assembly
50
′ detects the wavefront of outgoing beam
33
when lenslet array
51
divides the wavefront of outgoing beam
33
into sub-apertures of the lenslets. Each lenslet forms a focal spot such as focal spot
52
on CCD camera
53
, and as is well known, the pattern of focal spots carries the signature of the wavefront of the beam to be measured.
In accordance with this prior art design, output from CCD camera
53
is applied as input to analyzer
60
, for example, a personal computer. Analyzer
60
then determines the x, y, z position of a centroid of each of the focal spots in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Next, analyzer
60
determines the slope of each beam segment using the coordinates of the centroids to determine the slope of a portion of the beam passing through each of the elements of lenslet array
50
. Next, analyzer
60
uses any one of a number of methods that are well known to those of ordinary skill in the art to use the slopes of the beam segments to reconstruct the wavefront of beam
33
at plane P′. For example, in one such embodiment, analyzer
60
fits the slopes of the beam segments to a set of Zernike polynomials to reconstruct the wavefront of beam
33
at plane P′ in accordance with the teaching of an article entitled “Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor” by J. Liang et al.,
J. Opt. Soc. Am. A,
Vol. 11, No. 7, July 1994, pp. 1949-1957, and an article entitled “Aberrations and retinal image quality of the normal human eye” by J. Liang et al.,
J. Opt. Soc. Am. A,
Vol. 14, No. 11, November 1997, pp. 2873-2883 (the “Liang articles”), which Liang articles are incorporated by reference herein. The wavefront of outgoing beam
33
is then reconstructed at plane P via a scale factor determined by relay optics assembly
40
. A review of the Hartmann-Shack wavefront sensor, and wavefront reconstruction is found in U.S. Pat. No. 5,777,719. Finally, the refractive errors of the eye are calculated by analyzer
60
in accordance with any one of a number of methods that are well known to those of ordinary skill in the art using the reconstructed wavefront. For example, one such method is disclosed in a publication of Frey et al. on Jun. 3, 1999, WO 99/27334 entitled “Objective Measurement and Correction of Optical Systems Using Wavefront Analysis” wherein distortions of the wavefront are taken as an estimate of the aberrations, which publication is incorporated by reference herein (see also the Liang articles). An algorithm for use in analyzer
60
, for example, a computer algorithm, is commercially available from, for example, Adaptive Optics Associates of Cambridge, Mass.
Comprehensive measurement of the refractive errors of the eye's optics provided by prior art wavefront refractor
200
include high order aberrations. Such comprehensive measurement of the refractive errors can be used to guide laser surgery to correct the refractive errors of the eye. Advantageously, a wavefront refractor can provide more accurate measurement of the refractive errors of an eye than a conventional auto-refractor. Consequently, a wavefront refractor may eventually be used to provide prescriptions for eyeglasses and contact lenses.
However, several problems arise in using prior art wavefront refractor
200
which includes Hartmann-Shack sensor assembly
200
. A first problem arises because refractive errors of a human eye can be substantial, and as a result, wavefront distortion can be significant. For the case of a planar wavefront produced by an emmetropic eye, focal spots
52
form a grid pattern on CCD camera
53
that is identical to that of lenslet array
51
. However, for a case where wavefront distortion is significant, the grid pattern of focal spots
52
may be badly distorted. This causes a need for an algorithm (used to analyze the grid pattern of focal spots) to associate each focal spot with the particular lenslet used to form the focal spot.
A second problem arises because distortion of the grid pattern of focal spots can arise from a source other than refractive error of the eye. In particular, the intensity distribution of the outgoing beam can vary significantly across the exit pupil due to a number of effects, including, for example, the scattering nature of the probe beam from the retina. In such a case, some focal spots (referred to herein as “bad” spots) may have their centroid shifted away from their chief rays—such a shift occurs whenever the intensity distribution across a lenslet has a strong slope. This causes a need for an algorithm (used to analyze the grid pattern of focal spots) to reject these shifted or “bad” spots.
A third problem arises because unwanted trace beams, i.e., beams reflected, for example, from optics elements and/or the eye, can not always be removed. In such a case, “ghost” focal spots may appear in the grid pattern of focal spots. This causes a need for an algorithm (used to analyze the grid pattern of focal spots) to identify these ghost spots.
U.S. Pat. No. 5,629,765 (the '765 patent) discloses a spot matching technique that moves a CCD camera longitudinally, and records images in severa
Carl Zeiss, Inc.
Einschlag Michael B.
Manuel George
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